Business, Basis of Presentation and Summary of Significant Accounting Policies - Transition Table - Income Statement (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums	$ 11,230	$ 17,332			$ 32,497	$ 39,505
Universal life and investment-type product policy fees	1,334	1,275			3,911	3,959
Other revenues	606	728			1,866	2,003
Net investment gains (losses)	(927)	(411)			(2,650)	(1,610)
Net derivative gains (losses)	(1,202)	(226)			(2,289)	(2,147)
Total revenues	15,866	22,283			47,877	53,162
Policyholder benefits and claims	11,130	17,603			32,811	40,392
Policyholder liability remeasurement (gains) losses		136				94
Market risk benefit remeasurement (gains) losses	(796)	(965)			(1,425)	(3,162)
Interest credited to policyholder account balances	1,658	1,014			5,455	2,167
Policyholder dividends	153	158			463	551
Other expenses	3,204	2,922			9,394	8,782
Total expenses	15,332	20,868			46,656	48,824
Income (loss) before provision for income tax	534	1,415			1,221	4,338
Provision for income tax expense (benefit)	39	248			233	617
Net income (loss)	495	1,167	$ 493	$ 2,554	988	3,721
Net Income (Loss) Attributable to Noncontrolling Interest	6	5			17	15
Net income (loss) attributable to MetLife, Inc.	489	1,162			971	3,706
Net income (loss) available to MetLife, Inc.’s common shareholders	422	1,098			806	3,550
Comprehensive income (loss)	(3,373)	(3,253)			(661)	(16,357)
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	6	5			1	12
Comprehensive income (loss) attributable to MetLife, Inc.	$ (3,379)	$ (3,258)			$ (662)	$ (16,369)
Basic	$ 0.56	$ 1.38			$ 1.05	$ 4.38
Diluted	$ 0.56	$ 1.37			$ 1.05	$ 4.35
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums		$ 17,547				$ 40,039
Universal life and investment-type product policy fees		1,302				4,236
Other revenues		730				2,006
Net investment gains (losses)		(414)				(1,617)
Net derivative gains (losses)		(480)				(2,534)
Total revenues		22,270				53,582
Policyholder benefits and claims		17,993				40,976
Policyholder liability remeasurement (gains) losses		0				0
Market risk benefit remeasurement (gains) losses		0				0
Interest credited to policyholder account balances		980				2,102
Policyholder dividends		155				546
Other expenses		2,723				8,826
Total expenses		21,851				52,450
Income (loss) before provision for income tax		419				1,132
Provision for income tax expense (benefit)		19				(80)
Net income (loss)		400				1,212
Net Income (Loss) Attributable to Noncontrolling Interest		5				16
Net income (loss) attributable to MetLife, Inc.		395				1,196
Net income (loss) available to MetLife, Inc.’s common shareholders		331				1,040
Comprehensive income (loss)		(10,923)				(38,405)
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest		5				13
Comprehensive income (loss) attributable to MetLife, Inc.		$ (10,928)				$ (38,418)
Basic		$ 0.42				$ 1.28
Diluted		$ 0.41				$ 1.28
Revision of Prior Period, Accounting Standards Update, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums		$ (215)				$ (534)
Universal life and investment-type product policy fees		(27)				(277)
Other revenues		(2)				(3)
Net investment gains (losses)		3				7
Net derivative gains (losses)		254				387
Total revenues		13				(420)
Policyholder benefits and claims		(390)				(584)
Policyholder liability remeasurement (gains) losses		136				94
Market risk benefit remeasurement (gains) losses		(965)				(3,162)
Interest credited to policyholder account balances		34				65
Policyholder dividends		3				5
Other expenses		199				(44)
Total expenses		(983)				(3,626)
Income (loss) before provision for income tax		996				3,206
Provision for income tax expense (benefit)		229				697
Net income (loss)		767				2,509
Net Income (Loss) Attributable to Noncontrolling Interest		0				(1)
Net income (loss) attributable to MetLife, Inc.		767				2,510
Net income (loss) available to MetLife, Inc.’s common shareholders		767				2,510
Comprehensive income (loss)		7,670				22,048
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest		0				(1)
Comprehensive income (loss) attributable to MetLife, Inc.		$ 7,670				$ 22,049
Basic		$ 0.96				$ 3.10
Diluted		$ 0.96				$ 3.07